Stackable armchair



FIG. 1 is a front perspective view of a stackable armchair showing my new design;

FIG. 2 is a front and left side perspective view thereof;

FIG. 3 is a rear perspective view thereof;

FIG. 4 is a left side perspective view thereof;

FIG. 5 is a top perspective view thereof; and

FIG. 6 is a bottom perspective view thereof.

The side of the chair not shown is a mirror image of the side shown in FIG. 4. 

The ornamental design for a stackable armchair, as shown and described. 